1 Technical Field of the Invention
The present invention relates generally to tire inflation pressure sensing apparatuses or sensors. More particularly, the invention relates to a direct-type tire inflation pressure sensing apparatus which is configured to sense inflation pressures of tires of a vehicle and has a function of detecting the location of each of the tires in the vehicle.
2 Description of the Related Art
Conventional direct-type tire inflation pressure sensing apparatuses generally include a plurality of transmitters and a receiver.
Each of the transmitters is directly installed to one of a plurality of wheels of a vehicle and includes a pressure sensor working to sense an inflation pressure of a tire mounted on the wheel. Each of the transmitters is configured to send out a pressure signal representative of the inflation pressure of the tire sensed by the pressure sensor.
The receiver is installed to the body of the vehicle and includes at least one antenna. The receiver is configured to receive the pressure signals sent out from the transmitters through the at least one antenna and determine inflation pressures of tires of the vehicle based on the respective received pressure signals.
In the above arrangement, in addition to the pressure signals sent out from the transmitters, the receiver may also receive signals that are sent out from signal sources located outside the vehicle. However, it is impossible for the receiver to determine whether a signal received thereby has been sent out from one of the transmitters or from a signal source located outside the vehicle.
Moreover, it is impossible for the receiver to detect the location of each of the transmitters (i.e., each of the tires) in the vehicle. In other words, the receiver cannot determine from which one of the transmitters a pressure signal received thereby has been sent out.
To solve the above problems, Japanese Patent No. 3212311, an English equivalent of which is U.S. Pat. No. 5,602,524, proposes an approach.
According to the approach, each of the transmitters is configured to send out an ID signal representative of the identity thereof together with the pressure signal. On the other hand, the receiver is configured to have reference ID signals registered therein, each of which coincides with one of the ID signals sent out from the transmitters.
The receiver works to compare an ID signal received thereby with the reference ID signals registered therein and identify the transmitter from which the ID signal has been sent out when the ID signal coincides with one of the reference ID signals.
Consequently, the receiver can detect the location of the tire corresponding to the identified transmitter in the vehicle. More specifically, the receiver can determine whether the tire is mounted on a front-right, a front-left, a rear-right, or a rear-left wheel of the vehicle. Further, the receiver can determine the inflation pressure of the tire based on the pressure signal accompanying the ID signal.
However, according to the approach, each of the transmitters necessitates an ID signal specific thereto, and it is required to previously register reference ID signals in the receiver.
Moreover, as tire replacement or rotations are performed, it is required to newly register reference ID signals in the receiver. However, the registration of reference ID signals in the receiver is a time-consuming task and necessitates some additional devices.